Timing is critically important for restoration or channel additions in an optical network. For example, following a fiber cut, achieving layer 0 (optical) restoration within a short given time is critical to network operators and customers. If services can be restored within a short time (e.g., <=1 min), that means higher layer routers and their switch ports can be made available for carrying more traffic instead of reserving them for protection. Commonly-assigned U.S. Pat. No. 10,050,737, issued Aug. 14, 2018, and entitled “Methods and apparatus for pre-programming layer-0 service turn up speeds for photonic service provisioning or restoration,” the contents of which are incorporated herein, describes pre-programming restoration speeds for a given path.
Knowing future traffic demands, pre-planning for restoration to see if that layer 0 restoration can always be achieved within a short and strict time-limit such as 10 s, 60 s, etc. is a multi-dimensional problem. There is a need to know viable routes available for both home and restoration. Pre-selecting home-route based on latency, k-shortest path, diversity is not good enough, as equal priorities need to be assigned for selecting restoration paths due to the time-constraint restoration aspects. Link budget penalties have the biggest impact when selecting faster restoration speeds as the existing in-service channels on a restoration path will need to survive transients momentarily due to faster restoration activity. Hence, there is a need for additional margin requirement for pre-existing channels on a restoration path to allow fast restoration activity to meet the given time-constraint. In order to limit the link budget exposure, specific network engineering is required for any network based on the demands' capacity and reach. Such network engineering may include balancing the loads with specific spectrum assignment between home and restoration routes.
Hence, the challenge becomes, knowing future traffic demands, how the home and restoration routes can be selected, along with spectrum assignments for those demands so that a guaranteed time-constrained restoration can be achieved for any fiber cuts on the home route without costing too much additional link budget penalty on existing traffic.
There is no conventional approach for 1) a time-constrained Routing and Spectrum Assignment (RSA) for layer 0, i.e., how to restore or add channels within a fixed given time, 2) margin penalty-constrained RSA, i.e., to ensure existing channels on a restoration path do not experience more than a given penalty due to fast transients of a restoration activity, and 3) pre-planning of restoration speeds per route or per service to guarantee the time-constraint.